The present invention relates to a turbocharger.
Conventionally, turbochargers have been used, which utilizes kinetic energy of exhaust gas discharged by internal combustion engines to supercharge air to the engines. A typical turbocharger includes a turbine located in the exhaust system of an internal combustion engine and a compressor located in the intake system of the engine. When drawn into the turbine, exhaust gas discharged by the engine rotates the turbine impeller in the turbine. The turbine impeller is coupled to a compressor impeller located in the compressor. Thus, rotation of the turbine impeller rotates the compressor impeller. When the compressor impeller rotates, air drawn in through the compressor inlet is compressed and then delivered to the diffuser passage arranged outward of the compressor impeller. The air is subsequently delivered to a scroll passage. The supply of compressed from the compressor to the internal combustion engine improves the performance of the engine.
An inlet for blow-by gas discharged by the internal combustion engine is provided on the upstream side of the compressor inlet. Blow-by gas refers to gas that has leaked, for example, through clearances between the pistons and the cylinders in an internal combustion engine. Blow-by gas contains lubricating oil and fuel. The air drawn in through the inlet is compressed to become high-pressure compressed air. This increases the temperature of a wall surface that faces the diffuser passage, that is, the diffuser surface, through which the compressed air flows. Droplets containing oil as a main component are solidified at temperatures higher than or equal to, for example, 160° C. Thus, oil and the like are solidified and accumulated on the diffuser surface. Accumulation of oil and the like reduces the area of the diffuser passage, reducing the performance and operating characteristics of the turbocharger.
Japanese Patent No. 5359403 discloses a configuration in which a cooling passage is provided in a compressor housing member. Fluid that flows through the cooling passage cools the diffuser surface, thereby lowering the temperature of the diffuser surface. Accordingly, the temperature of the diffuser surface is kept lower than the temperature at which oil and the like are solidified. This limits solidification of oil and the like on the diffuser surface.
However, since the cooling passage disclosed in Japanese Patent No. 5359403 is provided in the wall of the compressor housing member along the diffuser surface, production of the cooling passage is significantly complicated.